Question. Will this car ever see the track? You said that you are getting understeer in the twisties. So it's street. Track set-up on the street will KILL tire life. Pick your poison. You screwed up on your front tire size.
Should have went with a 275/35-19. And now you want a work around. Ain't going to happen. Get the SPL upper control arms. For the street. Front camber at -2.0, caster at +6 to +7, toe should be 1/16" in. Rear camber at -1.75, rear toe at 1/16" in. If you set the rear toe to zero, and out. You will get a condition called snap-oversteer. It doesn't happen all the time, but when is does. You will be cleaning out your shorts!
It's scary when you are looking at the guy behind you, eyeball to eyeball.
Front sway bar full stiff, rear bar full soft. The front of the Z has too much roll in it. You WILL have to change the dampening on your coilovers. If not. You are SCREWED! If you are not willing to make changes. You are doomed!
My set-up. I'm running bigger tires then most anyone.
Front 285/35-19 PS4S on 19x9.5, +25. Rear 345/30-19 PSS on 19x12, +28.
Front camber -2.5, caster +6.5, 1/16" toe in.
Rear camber -1.8, 1/16" toe in.
Hotchkis front sway bar, stock rear sway bar.
Rear diff is a OS Giken set-up at a 1.5 way, with 70% lock up.
My whole suspension is out of the SPL catalog. No rubber bushings.
I turn off my VDC and have done the YAW sensor mod too.
My Z likes to dart around. It's a bit nervous.